Broad band electronic switch



March 24,1959 J. CART ER ETAL 2,879,485.

BROAD BAND ELECTRONIC SWITCH Filed April 6. 1956 DUPLEXER ITTlNG SOURCETRANSM RECEIVER INVENTORS, JOHN 1.. 04mm BY 4 IRVING RsllvaoLb.

A TTORNE Y BROAD BAND ELECTRONIC SWITCH John L. Carter, Neptune, andIrving Reingold, West Deal,

N.J., assignors to the United States of America as represented by theSecretary of the Army Application April 6, 1956, Serial No. 576,747 3Claims. (Cl. 333--13) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment of anyroyalty thereon.

This invention relates to a broad band electronic switching deviceparticularly useful in high level energy microwave apparatus where atransmitter and receiver must be alternately connected to an antenna athigh speeds such as in the operation of a radar system. In many suchsystems it becomes either necessary or desirable that the operatingfrequency be shifted thru a relatively wide band. In microwave systemshaving conventional switching devices it is difficult or impossible tomaintain normal operating conditions thruout a wide band of frequenciesunless a complicated tuning system is empioyed in the switching device.The present invention enables a system to be operated successfully andeliiciently thru a wide range of frequencies with no physical change inthe switching device. The range of operating frequencies may be as broadas the spectrum embraced by the waveguide or other carrier of energyemployed in the system.

The invention has Wide application for use in various circuits and inconjunction with numerous microwave energy generating devices, theenergy outputs of which are tunable thruout a relatively wide range offrequencies, such as magnetrons, carcynotrons, traveling wave tubes,klystrons and similar devices. An important capability of the inventionlies in the fact that it is especially well adapted for use inconnection with electronically tunable generators such as the voltagetunable magnetron.

The device of the invention consists of two main elements within awaveguide or other energy conducting structure. The first element isabroad band cavity resonator such as a pre-transmit-receive tubecommonly designated a pre-TR tube. Tubes of this type have various formsand for purposes of the invention this tube may be of that type known asthe multi-iris encapsulated window type. However, any resonant broadband pre- TR tube can be used such as a pre-TR tube having twomulti-iris windows separated by a quarter wavelength tube body. Forpurposes of description the encapsulated window type will be describedand illustrated herein.

The pre-TR tube above referred to is exposed to high level energy from agenerator or any source of such energy and functions in the conventionalmanner to transmit the major portion of the energy into one channel andblock the passage of energy to a second channel. At the same time thistube passes a small amount of leakage energy into the second channel. Itis the function of a second element in the second channel to attenuateor absorb this leakage energy and to prevent all or substantially all ofthe leakage energy from flowing therein.

The second element must be capable of attenuating the leakage energythruout a broad band of frequencies at least as great as the band offrequencies embraced by the first element. This second element is a gasfilled nited States Patent M 2,879,485 Patented Mar. 24, 1959 attenuatortube situated within the second channel of the energy conducting systemin such position that it will receive all of the leakage energy from thefirst element and must have a gas content so adjusted as to break downat the energy level of the leakage component and moreover the attenuatortube must respond to energy thruout the stipulated broad frequency bandof the system. A further component of the attenuator tube is a magneticelement designed to embrace the tube and apply a field of varyingstrength along the tube to efiect ionization of the. gas therein. Thismagnetic element insures that gyromagnetic resonance will occur thruoutthe he quency band in use. An alternative structure for the secondelement would provide an attenuator tube having external triggeringmeans. Thus energy in the system is under control of the switch whichfunctions efficiently thruout a wide band of frequencies.

It should be particularly pointed out that the applied magnetic fieldreduces the energy level at which the attenuator tube may be made tofire by a large factor compared to its breakdown point without thefield. This ratio may be as high as fifty to one; The action of themagnet therefore contributes in large part to the success of theinvention by enabling the attenuator tube to respond to the relativelylow energy level of the leakage energy.

it is a primary object of the invention to provide electronic switchingof microwave energy over a broad band of frequencies.

A further object of the invention is to provide broad band microwaveswitching capable of controlling high level microwave energy to anextent which affords complete protection and permits operation ofsensitive low power devices connected in the system.

A still further object of the invention is to provide an electronicswitching device substantially uniformly effective thruout the operatingfrequency of the waveguide or other energy conducting means in which itis used.

A further object of the invention is to provide an electronic switchingmeans having an attenuating device capable of being activated at verylow energy levels thereby to attenuate leakage energy passed by a pre-TRtube.

A still further object of the invention is to provide a switching devicereliable in operation and exceptionally rugged and long-lived.

Other objects and features of the invention will more fully appear fromthe following description and will be particularly pointed out in theclaims.

To present a better understanding of the invention a particularembodiment thereof will be described and illustrated in the accompanyingdrawings, wherein Fig. l is a diagrammatic representation of one type ofapparatus in which the device may be used.

Fig. 2 is a longitudinal cross-section on line 22, Fig. 3.

Fig. 3 is an end elevation of the device.

The invention may be utilized in many applications requiring microsecondswitching of high level microwave energy. As a typical example of theuse of the invention the following description presents the invention inconnection with radar systems. In the design of radar systems theproblem of the inherent operating bandwidth thereof presents certainlimiting conditions which are diflicult to overcome. In many radarsystems and also in systems. other than radar, it is highly advantageousto operate the apparatus at diflferent frequencies at different times.This fact coupled with the fact that conventional switching or duplexingdevices function efiiciently within a narrow frequency band onlyrestricts conventional systems to narrow band operation. The

invention, on the other hand, affords efiicient switching and thenecessary protection to delicate receiving elements or other devices inthe system thruout a wide band of operating frequencies.

Referring to the drawings in Fig. l a switch or duplexer 5 constructedin accordance with the invention is shown as inserted in a conventionalradar circuit containing a magnetron 6 or other microwave generator, anantenna 7 and a receiver 8. As in conventional duplexing devices powergenerated by the magnetron, in pulsed form, acts to short-out thatportion of the circuit leading to the receiver thus affording protectionfor the receiver during the transmitting period. The echo pulse pickedup by the antenna is then prevented from traveling to the magnetron andis switched into the receiver 8 in the con ventional manner passingfreely thru the duplexer.

The switching unit or duplexer 5 is of special construction asillustrated in Figs. 2 and 3 of the drawings and is composed of two mainelements arranged in series in the waveguide 9. The first element is abroad band resonant pre-TR device constructed and arranged to be exposedto high level energy in the system and becomes ionized by such energy.The gas content and the physical conformation of this device is adjustedto function over a wide band of frequencies and moreover the gas contentshould be such that a predetermined leakage current will pass therethrufor reasons to be pointed out hereinafter. This first element may be amulti-iris gas filled encapsulated window. Any resonant broad bandpre-TR tube may be used. As shown in the drawings the first elementconsists of a multi-iris window 10 extending laterally across thewaveguide 9. The window is composed of a metal plate 11 desirably madeof Kovar or similar material having suitable thermal expansioncharacteristics matching that of the glass windows 12 which are sealedinto openings in the plate 11. The edges of a glass member 13 are fusedinto contact with the plate 11 to form a chamber 14 embracing thewindows 12.

The chamber 14 is exhausted and filled with an appropriate gas fillingsuch as argon plus water vapor at a pressure between and 50 mm. ofmercury. The gas content should be adjusted to permit leakage energy topass therethru at a level sufficient to ionize the gas content in thesecond element. The level of this leakage energy should not, however,exceed that which the second element may safely absorb.

The second element is an attenuating device capable of absorbing theleakage energy which passes thru the first element and comprises anattenuator tube 15 within the waveguide and spaced a short distance fromthe first element. This attenuator tube can be an externally triggered,broad banded, cold cathode device or it may be a self-triggered devicein which the frequency at which breakdown occurs therein is controlledby a shaped magnetic field. The latter type of device is shown in thedrawings and utilizes either a solenoid type electromagnet or apermanent magnet. For best operation it has been found that when theoperating frequency is less than 3000 me. an electromagnetic solenoidmay be used having windings designed to produce a tapered magnetic fieldextending along the flow of energy within the tube and energized from anexternal source. At frequencies exceeding 3000 me. a more suitable meansfor supplying the magnetic field has been found to be a permanent magnet16 shown in the drawings. This magnet may have a horse-shoe shapedcross-section as shown in Fig. 3 and embrace the full length of theattenuator tube preferably extending somewhat beyond the ends thereof toeliminate fringing field effects. The magnet also is tapered in itsdimension parallel to the waveguide thereby to impose a shaped ortapered magnetic fieeld upon the gas within the tube. Such a structuremay be designed to produce proper gyromagnetic resonance over a broadfrequency band. This relationship of the field strength of the magnetand operating frequency may be expressed as follows:

where H is the field strength in gauss required for gyromagneticresonance to occur and f is the transmitter signal frequency inmegacycles. The length of the magnetic field should be of the order oftwo wavelengths of the nominal resonant frequency of the waveguide inuse.

The invention functions as follows. A high energy RF pulse from themagnetron or other source of power acts to ionize the gas in the firstelement; namely, the pre-TR tube thus cutting off substantially all ofthe flow of energy into the waveguide 9. The amount of leakage energywhich passes the first element is controlled by the particular gascontent of the element and moreover since the first element is a broadband device it will fire at any frequency within its particular spectrumand consequently the leakage frequency may also be of any value withinthat spectrum. The second element is adjusted to break down or fire atthe level of the leakage energy. The attenuator tube 15 also has thenecessary capacity to absorb all or substantially all of the leakageenergy. This control is effective at any wavelength within the bandembraced by the device which, as suggested above, may be substantiallyequal to that of the bandwidth of the waveguide itself. The magnet 16acts to permit gyromagnetic resonance at any frequency within the band.

What is claimed is:

1. A duplexer for microwave energy connected in a system where it isexposed to the maximum energy output level of a microwave generatorcomprising, a waveguide, a transmit-receive electronic switching meansin said waveguide having a resonant broad band cavity with a gas contentadjusted to ionize at the generator output energy level, attenuatingmeans in said waveguide on the low energy level side of saidtransmit-receive switching means, said attenuating means consisting ofan elongated energy permeable inclosure having a gas content adjusted toionize at the low level of the leakage energy from said transmit-receiveswitching means and a magnet embracing said inclosure, said magnethaving a tapering flux density along its length whereby the varyingfield intensity applied to the leakage energy present in the inclosurewill expand the band of frequencies which are absorbed within theinclosure.

2. In combination with means to conduct microwave energy from a sourceof energy to at least two channels, an electronic switching devicecomprising a transmitreceive resonant cavity exposed to the maximumenergy from said source, said cavity having a predetermined high ratioof incident to leakage energy, said transmit-receive cavity acting topass all but a small portion of the energy to a first channel and tostop all except a small amount of leakage energy from passing to asecond channel, attenuating means positioned in said second channel toreceive leakage energy only from said transmit-receive cavity consistingof an elongated attenuator tube of energy permeable material having agas content ionizable at the leakage energy level and having anabsorption capacity sufiicient to attenuate the leakage energy and anelongated magnet embracing said attenuating tube said magnet acting toapply a field to said tube varying in intensity along the path of energyflow, said gas content and magetic field being calculated to causeionization of the gas content through-out a broad band of frequencies.

3. In combination with a microwave energy conducting system operable toconduct energy from a source to at least two channels, an electronicswitching device comprising a first transmit-receive resonant cavityexposed to the maximum energy from said source said resonant cavitybeing constructed to function thruout a broad band of frequencies of theorder of the operating band of frequencies of said conducting systemsaid cavity having a predetermined high ratio of incident to leakageenergy, said transmit-receive cavity acting to pass most of the highlevel energy to a first channel and to stop all but the leakagecomponent thereof which passes to the second channel, attenuating meansin said second channel on the low energy side of said first resonantcavity consisting of an elongated attenuating tube of energy permeablematerial in said second channel containing a gas content ionizable atthe leakage energy level and having an absorption capacity at leastsufficient to absorb the leakage energy and an elongated magnetconstructed to produce a field of varying intensity thruout its length,

said magnet being positioned to apply its varying flux along thedirection of energy flow in said attenuator tube.

References Cited in the file of this patent I UNITED STATES PATENTS2,519,795 Smullin Aug. 22, 1950 2,748,35l Varnerin May 29, 19562,776,412 Sparling Jan. 1, 1957 OTHER REFERENCES Ararns: MicrowaveApplications of Gas Discharges, Electronics, November 1954, pages 16872. Copy in R0. Library.

